As shown in FIGS. 28 and 29, conventionally there is a printed wiring board having a mounting portion 970 for mounting electronic parts to an insulating substrate 97 and a conductor circuit 96 arranged around this mounting portion 970. A bonding pad portion 969 forming an end tip of the conductor circuit 96 is formed near the mounting portion 970. A pad portion 961 for joining a soldering ball, etc. is formed in the conductor circuit 96.
The mounting portion 970 is constructed by a concave portion surrounded by a mounting hole 971 formed in the insulating substrate 97 and a heat radiating plate 98 covering one end of the mounting hole 971.
As shown in FIG. 29, a surface of the insulating substrate 97 is covered with an insulating film 91 except for the pad portion 961 and the bonding pad portion 969. In other words, this insulating film 91 exposes the pad portion 961 and the bonding pad portion 969 by arranging an opening portion 910 above the pad portion 961 and the bonding pad portion 969.
A manufacturing method of the above printed wiring board will be explained next.
First, as shown in FIG. 30, a mounting hole 971 is bored in an insulating substrate 97 which is sticking a copper foil thereto. Next, the copper foil is etched so that a conductor circuit 96 having a pad portion 961 and a bonding pad portion 969 is formed.
Next, as shown in FIG. 28, solder resist constructed by thermosetting resin is printed on a surface of the insulating substrate 97. At this time, surfaces of the above pad portion 961 and the bonding pad portion 962 are exposed as they are without the solder resist printing.
Next, the solder resist is thermally cured and is set to an insulating film 91.
Thereafter, a heat radiating plate 98 is adhered to the surface of the insulating substrate 97 by using an adhesive 981 so as to cover one end of the mounting hole 971.
Thus, a printed wiring board 9 is obtained.
However, the above conventional manufacturing method of the printed wiring board 9 has the following problems.
Specifically, as shown in FIG. 31, except for a portion of the pad portion 961 no very small opening portion 910 can be formed in the insulating film 91 in a method for partially printing the above solder resist. Therefore, it is impossible only to expose a very small portion in the conductor circuit 96. As a result, no high density mounting can be improved.
In contrast to this, a manufacturing method as shown in FIG. 32 is proposed. In this method, an entire surface of the insulating substrate 97 forming the conductor circuit 96 therein is covered with a solder resist 912 constructed by an optical curing type resin. The solder resist 912 is exposed in a state in which a light interrupting mask 94 is arranged above an opening portion forming portion.
In this method, the solder resist 912 in a portion of light 940 interrupted by the mask 94 is not cured and is left as it is. In this state, the solder resist in an exposed portion is cured and forms an insulating film. Next, the insulating substrate 97 is dipped into a developing liquid and the solder resist in an uncured portion is removed from the insulating substrate 97. Thus, an opening portion 910 is formed in the cured insulating film 91 and one portion of the conductor circuit 96 is exposed.
However, in this method, since the optical curing type resin used as the solder resist has a property of absorbing humidity, no solder resist is suitable as the insulating film.
Further, since the above light has scattering light, the above light cannot be sufficiently interrupted so that no opening portion 910 can be formed in a sharp state. Therefore, for example, it is almost impossible to form a very small opening portion having a size equal to or smaller than 0.60 mm. Therefore, no high density mounting can be improved.
By using a drill there is also the method for boring a hole for conductivity. However, in this case, it is also difficult to form a very small hole for conductivity.
Further, there is a case in which various kinds of conductive members are formed around the hole for conductivity. Tangibly, such conductive members are constructed by a land surrounding a peripheral portion of the hole for conductivity, a pad for externally joining a soldering ball, a plating lead for forming electric plating, etc. High density is also desirable when these conductive members are formed.
With consideration to such conventional problems, the present invention provides a printed wiring board able to form an insulating film having a very small opening portion and be mounted at high density, and a manufacturing method of the printed wiring board.